You will have to get an import export license on both ends. Lots of paper work, takes time, and there are fees associated. In the US you can find the needed info on the USFW site, look for a similar Canadian site and you should be able to find something. They have to be shipped to an Point of Entry Airport for customs inspection too.
IMO if your not selling a few thousand dollars worth of t's to someone it isnt worth the hassle.